Effects of microwave condition on the formation and characteristics of TiO2 submicron-sized beads and its use in all-plastic flexible dye-sensitized solar cells

Carbon and/or nitrogen doped TiO2 mesoporous beads have been prepared using hexamethylenetetramine as the dopant source in a microwave-assisted hydrothermal synthetic route. It is found that the hydrothermal time has pronounced effects on the crystallinity, grain size, and carbon and/or nitrogen incorporation into the TiO2 lattices. The carbon and/or nitrogen doping creates interband localized states above the valence band of TiO2 and therefore enhances the optical response of TiO2 in the visible light region. Selected carbon and/or nitrogen doped TiO2 mesoporous beads are made into flexible dye-sensitized solar cells (FDSSCs), which are analyzed by solar simulator, electrochemical impedance spectroscopy, intensity modulated photocurrent/photovoltage spectroscopy, and incident photon-to electron conversion efficiency. The photoelectrode consisting of the doped TiO2 mesoporous beads shows improved FDSSCs due to the better electron injection and collection efficiencies. The electron lifetime is also relatively high, indicating that the doping does not introduce recombination. Overall speaking, both improved optical and electronic properties are demonstrated and discussed in depth.